Klotho is a type-I transmembrane protein that is associated with many functions. A novel ß-glucuronidase, Klotho has been associated with phosphate regulation, organ protection, and aging, among others. Though a single gene, it has three major isoforms: the transmembrane form, a shed soluble form, and a truncated soluble form. The extracellular portion of the protein consists of two glycosyl hydrolase domains referred to as KL1 and KL2. Upon cleavage at the base of the extracellular domain the protein becomes the shed soluble form and is an active form that functions as a hormone. Importantly, Klotho is a receptor and a co-receptor of the phosphate regulation protein FGF-23. While Klotho/FGF-23 homeostasis has primarily been focused on phosphate and vitamin D regulation, continuing research is associating Klotho and FGF-23 with functionality that impacts the heart, bones, blood vessels, and parathyroid gland.

The MicroVue Klotho assay is a sandwich enzyme immunoassay in a microtiter plate format utilizing a capture monoclonal anti-Klotho antibody specific to the KL2 region coated on the plate and a detection mouse monoclonal anti-Klotho antibody specific to the KL1 region.